Changes in motor vehicle internal combustion engines to improve fuel economy and/or to reduce carbon emissions have led to “undersized engines”—the utilization of smaller engines in vehicles that are larger than those smaller engines were originally intended to serve. Efforts to reduce friction, to reduce pumping work and to address other challenges have yielded engines having fewer combustion cylinders and/or smaller displacements than predecessor engines. At low load, the throttle of a traditional engine is substantially closed, reducing engine cylinder pressure. In such a situation the engine has to work to draw combustion air into the cylinders, thus causing a pumping loss that reduces engine efficiency and lowers fuel economy. Friction reduction has been achieved by reducing the number of combustion cylinders in engines and/or reducing the engine's displacement, again resulting in reduced engine power.
Turbochargers have been employed to improve engine torque, but have introduced a performance problem for drivers; turbocharged engines have suffered from turbo lag during acceleration. These new configurations thus naturally result in both lower power and poorer performance at tip-in and slow speeds. In addition to the negative impacts on performance, fewer cylinders and/or smaller displacements mean reduced engine power more generally. New ways have been sought to generate additional power to compensate for these deficiencies. Some solutions have utilized twin-scroll, dual-nozzle and variable-geometry turbochargers, which add complexity to an engine's operation and layout.
Some earlier engine systems have replaced conventional throttle butterfly valves with intake-valve-controlled throttling that uses an electrical, electromechanical and/or hydraulic mechanism to control individual intake valve lift for each cylinder to regulate combustion air flow into the cylinder. These systems use a stepper motor to control a secondary eccentric shaft fitted with a series of intermediate rocker arms, which in turn control the degree of valve lift. The throttle butterfly valve is no longer used to control the cylinder's combustion air supply, though for safety reasons it is still fitted as an emergency back-up. Thus these earlier systems have additional hardware the increases the complexity of crankshaft operation. Moreover, because the intake valves are used as combustion air control valves, tremendous spring and frictional valve spring forces and operational characteristics must be addressed and overcome with an intake valve throttling operation. These heavy spring and frictional forces diminish the responsiveness of these intake-valve-as-throttle systems.
Overview
Synergistic induction and turbocharging includes the use of one or more throttles in close proximity to each cylinder intake valve to control air flow in each intake port delivering air to combustion cylinders in an internal combustion engine system. A turbocharger may also be affixed in close proximity to each cylinder exhaust valve to enable a synergistic combination of hyper-filling cylinders with combustion air and immediate harvesting of exhaust gas by adjacent turbochargers. In some implementations the turbochargers may be low-inertia turbochargers. The combination of individual throttles per intake port and a turbocharger in close proximity to each cylinder enables faster ramp-up of an engine in the early stages of acceleration. These implementations and others described herein provide concomitant improvements in both fuel economy and engine performance. Frequently, improvements to fuel economy have imposed performance limitations and, similarly, improved engine performance has come with fuel economy degradation. More specifically, synergistic induction and turbocharging further improves fuel economy because “real time” torque is greater under acceleration conditions and provides various benefits, including (without limitation): the use of lower numerical axle ratios, lower “K” factor torque converters, earlier (i.e., lower engine RPM) shift schedules, and more time and operating modes with fuel delivery held to a 14.6 to 1 air fuel ratio.
In internal combustion engine systems utilizing cylinders having only one intake port, a throttle is affixed in close proximity to any intake valve(s) to control air flow through the intake port. In some implementations a turbocharger is affixed in close proximity to each cylinder's exhaust valve(s). The combination in these implementations of one throttle per intake port and one turbocharger per cylinder provide rapid filling of the cylinder with combustion air when the engine ceases idle operation and provides substantial improvement in turbocharger performance, in some instances eliminating perceptible turbo lag. In some implementations a standard turbocharging system can be used, which still provides improved ramp-up of the turbocharger.
In internal combustion engine systems utilizing cylinders having two separate intake ports for each cylinder, a throttle is affixed in close proximity to each intake port's intake valve(s) to control air flow through each intake port. An individual turbocharger can be affixed in close proximity to each cylinder's exhaust valve, in some cases using low-inertia turbochargers to further enhance turbocharger ramp-up. The dual-port throttles in each cylinder's induction system can be operated in unison (i.e., so that all throttles are either open or closed) or can be operated in a bifurcated or other manner. In some implementations bifurcated operation of the throttles can include opening only one throttle per cylinder when idle mode operation of the engine system ceases and maintaining single port air flow until peak single-port torque is reached, after which the second throttle in each cylinder intake can be opened to permit air flow through both intake ports at higher loads.
Close proximity of a cylinder's throttle mechanism to that cylinder's intake valve system can be characterized by the throttle-to-intake volume defined in an intake channel between any throttle(s) and their respective intake valve(s). The throttle-to-intake volume can be limited to 80% or less of the cylinder displacement or to 60% or less of the cylinder displacement in some implementations. Moreover, close proximity of a turbocharger to its respective exhaust valve(s) can be characterized by the exhaust-to-turbine volume defined in an exhaust channel between any exhaust valve(s) and the turbocharger's turbine inlet.
In both single-port and dual-port implementations, equalizing ports can be used to provide generally even distribution of combustion air during idle mode operation of the engine system. These ports can be passages interconnecting and allowing air flow between intake valves of the combustion cylinders and may, in some implementations, include equalizing port valves to close the equalizing ports whenever the engine system is not operating in idle mode. Moreover, balancing valves can be used to allow sharing of exhaust gas between turbochargers. These balancing ports can be passages interconnecting and allowing exhaust gas flow between exhaust valves of the combustion cylinders and may, in some implementations, including balancing port valves to prevent exhaust gas sharing.